Telecommunications apparatus and methods for communicating with a first and a second type of devices

ABSTRACT

A wireless telecommunications system including at least one base station, a first terminal device and a second terminal device, wherein the first terminal device is a terminal device of a first type and the second terminal device is a terminal device of a second type, the second type being different from the first type, and wherein the at least one base station is configured to communicate data which is specific to the first terminal device in a synchronous manner and to communicate data which is specific to the second terminal device in a non-synchronous manner.

BACKGROUND OF THE INVENTION

The present invention relates to methods, systems and apparatus fortransmitting data in mobile telecommunications systems.

Mobile communication systems have evolved over the past ten years or sofrom the GSM System (Global System for Mobile communications) to the 3Gsystem and now include packet data communications as well as circuitswitched communications. The third generation partnership project (3GPP)is developing a fourth generation mobile communication system referredto as Long Term Evolution (LTE) in which a core network part has beenevolved to form a more simplified architecture based on a merging ofcomponents of earlier mobile radio network architectures and a radioaccess interface which is based on Orthogonal Frequency DivisionMultiplexing (OFDM) on the downlink and Single Carrier FrequencyDivision Multiple Access (SC-FDMA) on the uplink.

Third and fourth generation mobile telecommunication systems, such asthose based on the 3GPP defined UMTS and Long Term Evolution (LTE)architectures, are able to support a more sophisticated range ofservices than simple voice and messaging services offered by previousgenerations of mobile telecommunication systems.

For example, with the improved radio interface and enhanced data ratesprovided by LTE systems, a user is able to enjoy high data rateapplications such as mobile video streaming and mobile videoconferencing that would previously only have been available via a fixedline data connection. The demand to deploy third and fourth generationnetworks is therefore strong and the coverage area of these networks,i.e. geographic locations where access to the networks is possible, isexpected to increase rapidly.

The anticipated widespread deployment of third and fourth generationnetworks has led to the parallel development of a class of devices andapplications which, rather than taking advantage of the high data ratesavailable, instead take advantage of the robust radio interface andincreasing coverage. One such class of device aremachine-type-communication (MTC) devices supporting machine-to-machine(M2M) communications. Examples include so-called smart meters which, forexample, are located in a customer's house and periodically transmitinformation back to a central MTC server data relating to the customer'sconsumption of a utility such as gas, water, electricity and so on.Further information on characteristics of MTC-type devices can be found,for example, in the corresponding standards, such as ETSI TS 122 368V10.530 (2011-07)/3GPP TS 22.368 version 10.5.0 Release 10) [2]. MTCdevices may in some respects be seen as devices which can be supportedby relatively low bandwidth communication channels having relatively lowquality of service (QoS), for example in terms of latency.

Whilst it can be convenient for a terminal such as an MTC-type terminalto take advantage of the wide coverage area provided by a third orfourth generation mobile telecommunication network there are at presentsome disadvantages associated with the use of existing networkconfiguration for communicating MTC data. The minimisation of powerconsumption and complexity is a driving factor behind all third andfourth generation terminals, and even more so for MTC terminals becauseof desired low cost and placement in locations where access to adedicated power source may be limited or not economically viable.Consequently, there is a desire to reduce the power consumption of MTCterminals.

A technique which has been incorporated into LTE to help manage powerconsumption is the so-called discontinuous reception (DRX) mode. DRXallows a terminal to stay in a sleep mode between paging cycles with thenetwork and therefore conserve power. This is achieved by extending theperiod of a paging cycle to a device and the device waking up for theduration of a predetermined wake-up window after a sleep period toreceive any paging information. This process can help relieve theterminal of frequent synchronisation and communication tasks with thenetwork and the reduced operating burden can lead to an associatedreduction in power consumption. Thus the DRX capability included inLTE-type systems enables devices to be brought out of a power savingidle state and re-establish communications with the network when needed.

Whilst the DRX operating mode can help reduce power consumption forterminals which might access the network only infrequently, there arenonetheless a number of drawbacks with this approach. Firstly, themaximum DRX cycle currently specified is relatively short, only around2.5 seconds. However, it is expected that some types of terminal, forexample MTC-type devices, might wish to communicate data much lessfrequently than this such that a longer potential period of inactivitycould be more appropriate in some circumstances. Secondly, when aterminal device wakes up in accordance with a conventional DRX operatingmode, the device must perform a number of steps before it is able todetermine if the network has data for communication to the device.

For example, when operating in a conventional DRX mode and a DRX timerexpires (i.e. when it is time for device to “wake up”), a device willcommonly be required to undertake the following steps to retrieve userdata.

Step 1: Frame Synchronization. The device searches for synchronizationsignals to achieve frame synchronization

Step 2: Reception of Master Information. The device determines thelocation of the Master Information Block (MIB) in the frame structureand decodes the MIB to determine channel bandwidth and System FrameNumber (SFN) information.

Step 3: Reception of System Information. Taking account of SFN, thedevice determines the location of System Information Block(s) (SIB) inthe frame structure and decodes SIB to obtain further system information

Step 4: Reception of Paging Message. The device searches for paginginformation that would indicate the presence of user data for the deviceon the relevant control channel (PDCCH).

Thus as part of each DRX cycle the device checks specific frames andsubframes for paging messages from the network, the locations of pagingmessages and the DRX cycle of a device having been pre-negotiatedbetween the device and the network. When a relevant paging message isreceived by a device, the device establishes a data connection with thenetwork using established signalling and proceeds to transmit/receivethe relevant data. However, as set out above, for the device to be ableto do this it needs to first perform various steps includingsynchronising with the network's frame structure.

In some cases a device may not be required to perform all theabove-mentioned steps on every DRX cycle. For example, for short DRXcycles, frame synchronisation could in principle be maintained from oneDRX cycle to the next with sufficiently accurate timing. Furthermore,information such as MIB/SIB may in principle be stored at the device andassumed the same in different DRX cycles such that some of the foursteps set out above may be abbreviated. However, for relatively long DRXcycles it is likely to be necessary to re-obtain this information for atleast some, if not most, DRX cycles.

Because a device will generally perform the above-identified steps (oran abbreviated version of them) for every DRX cycle, there can still bea significant amount of power required to operate in a DRX mode, evenduring extended periods when there is no data to be communicated to thedevice.

One existing low power, short-range ad-hoc network protocol designed forlow data-rate applications is ZigBee®. It is a protocol designed for usewith mesh networks and has the capability to forward messages betweendevices and for devices to sleep between periods of activity. To furtherconserve node battery life the transfer of data between a coordinatordevice and a receiving device is primarily controlled by the receivingdevice as opposed to the coordinator device. The protocol fortransferring data from a coordinator device to a receiving device isdependent upon whether the ZigBee network is beacon or non-beaconenabled. In a beacon-enabled network, the coordinator device indicatesin a beacon that it wishes to transfer data to a receiving device. Areceiving device periodically wakes up from its sleeping state, receivesand utilises the beacon for synchronisation, and then checks forrelevant messages from the coordinator device. If one is found, thereceiving device requests that the coordinator device sends the data. Ina non-beacon-enabled network, a receiving device periodically wakes froma sleeping state and requests any pending data from the coordinatordevice. If there is pending data the coordinator device acknowledges therequest for transmission and then sends the data. If there is no pendingdata the coordinator informs the device and the device responds with anacknowledgement. This protocol allows devices to sleep for significantperiods of time, but requires a number of two-way transmissions betweenthe devices and the coordinator to establish communications regardlessof whether or not there is data to be communicated. Furthermore, thesemodes of operation depart significantly from established wirelesstelecommunications principles and so could not be readily implemented ina wireless telecommunications system, such as an LTE-type network.

Some other types of network which allows a device to enter a sleepperiod/power saving mode are those based on the IEEE 802.11 standard,for example WiFi. In these networks a device may enter a sleep mode andthe network access point maintains a list of all the devices that arecurrently sleeping. A beacon frame that contains information on pendingdata for sleeping devices is then periodically transmitted by the accesspoint. Sleeping devices wake up and check this frame to learn whetherthere is data pending; if data is pending the devices poll the accesspoint and initiate communications with the access point. Communicationsbetween the device and access point can also be re-established by thedevice informing the access point that it has woken-up from a sleepperiod. Although this procedure allows a device to sleep for periods oftime and therefore save power, they still have to wake up at predefinedtimes to check the beacon frame and then perform a number of two-waycommunications to establish a link with the network. Consequently,devices need to maintain synchronisation with the network in order toutilise the power saving mode and when a device does emerge from thepower saving mode it incurs significant overheads. Furthermore, and aswith ZigBee, these operating aspects of schemes based on the IEEE 802.11standard depart significantly from established wirelesstelecommunications principles and so could not be readily implemented ina wireless telecommunications system, such as an LTE-type network

Thus although there are a number of established power saving techniquesfor devices which might infrequently receive only small quantities ofdata, there remains a need to provide improved schemes for reduced poweroperation for terminal devices operating in wireless telecommunicationsnetworks, for example MTC type devices operating in an LTE-type network.

SUMMARY OF THE INVENTION

In accordance with an aspect of the invention there is provided awireless telecommunications system comprising at least one base station,a first terminal device and a second terminal device, wherein the firstterminal device is a terminal device of a first type and the secondterminal device is a terminal device of a second type, the second typebeing different from the first type, and wherein the at least one basestation is configured to communicate data which is specific to the firstterminal device in a synchronous manner and to communicate data which isspecific to the second terminal device in a non-synchronous manner.

In accordance with some embodiments the at least one base station isconfigured to communicate data which is specific to the second terminaldevice in a non-synchronous manner only during time periods determinedin accordance with a predefined timing schedule.

In accordance with some embodiments the at least one base station isconfigured to communicate data which is specific to the second terminaldevice in a non-synchronous manner using a predefined frequency rangewhich is narrower than and within an operating frequency range for theat least one base station.

In accordance with some embodiments the data which is specific to thesecond terminal device comprises an indication of an identity of thesecond terminal device.

In accordance with some embodiments the data which is specific to thesecond terminal device comprises user-plane data for the second terminaldevice.

In accordance with some embodiments the data which is specific to thesecond terminal device comprises an indication of a coding scheme forthe user-plane data for the second terminal device.

In accordance with some embodiments the data which is specific to thesecond terminal device comprises an indication of a time and/orfrequency on which user-plane data for the second terminal device istransmitted by the at least one base station.

In accordance with some embodiments the at least one base station isconfigured to communicate data which is specific to the second terminaldevice in a non-synchronous manner by transmitting said data inassociation with a predefined signature sequence.

In accordance with some embodiments the at least one base station isconfigured to transmit the data which is specific to the second terminaldevice in a packet format for which the predefined signature sequencecomprises a portion selected from the group comprising a pre-ambleportion, a mid-amble portion, a post-amble portion, a pilot portion, anda scattered pilot portion.

In accordance with some embodiments the packet format further comprisesa header portion comprising an indication of an identity of the secondterminal device.

In accordance with some embodiments the packet format further comprisesa payload portion comprising user-plane data for the second terminal.

In accordance with some embodiments the at least one base station isconfigured to communicate data which is specific to another terminaldevice in a non-synchronous manner by transmitting said data specific tosaid another terminal device in association with the predefinedsignature sequence.

In accordance with some embodiments the at least one base station isconfigured to communicate data which is specific to another terminaldevice in a non-synchronous manner by transmitting said data specific tosaid another terminal device in association with another predefinedsignature sequence.

In accordance with some embodiments the predefined signature sequence isone of a set of predefined signature sequences for use by the at leastone base station for non-synchronously communicating data with terminaldevices of the second type.

In accordance with some embodiments the predefined signature sequence isone of a subset of the set of predefined signature sequences, andwherein the base station is configured to select one of the subset ofthe set of predefined signature sequences to be used fornon-synchronously communicating data with the second terminal device.

In accordance with some embodiments the second terminal device isconfigured to search transmissions from the at least one base station toidentity the predefined signature sequence and to determine if anidentified transmission of the predefined signature sequence isassociated with data which is specific to the second terminal device.

In accordance with some embodiments the second terminal device isconfigured to transmit acknowledgement signalling to the at least onebase station after successful receipt of the data which is specific tothe second terminal.

In accordance with some embodiments the at least one base station isconfigured to transmit a radio frame structure including a controlregion for control data for terminal devices of the first type, andwherein the at least one base station is configured to communicate withthe second terminal device at times and frequencies outside the controlregion for terminal devices of the first type.

In accordance with some embodiments the data which is specific to thesecond terminal device comprises an instruction for the second terminaldevice to proceed to synchronise to a frame structure transmitted by theat least one base station in order to receive further datasynchronously.

In accordance with some embodiments the at least one base station isfurther configured to communicate data with the second terminal devicein a synchronous manner.

In accordance with some embodiments the second type of terminal deviceis a machine-type communication, MTC, terminal device.

In accordance with some embodiments the wireless telecommunicationssystem is based around a 3rd Generation Partnership Project, 3GPP,architecture.

In accordance with another aspect of the invention there is provided amethod of operating a wireless telecommunications system comprising atleast one base station, a first terminal device and a second terminaldevice, wherein the first terminal device is a terminal device of afirst type and the second terminal device is a terminal device of asecond type, the second type being different from the first type, themethod comprising communicating data which is specific to the firstterminal device in a synchronous manner and communicating data which isspecific to the second terminal device in a non-synchronous manner.

In accordance with another aspect of the invention there is provided abase station for communicating data with a first terminal device of afirst type and a second terminal device of a second type, the secondtype being different from the first type, wherein the base station isconfigured to communicate data which is specific to the first terminaldevice in a synchronous manner and to communicate data which is specificto the second terminal device in a non-synchronous manner.

In accordance with another aspect of the invention there is provided amethod of operating a base station of a wireless telecommunicationssystem for communicating data with a first terminal device of a firsttype and a second terminal device of a second type, the second typebeing different from the first type, wherein the method comprisescommunicating data which is specific to the first terminal device in asynchronous manner and communicating data which is specific to thesecond terminal device in a non-synchronous manner.

In accordance with another aspect of the invention there is provided aterminal device for receiving data from a base station in use in awireless telecommunications system, wherein the terminal device isconfigured to receive data which is specific to the terminal device fromthe base station in a non-synchronous manner by searching a radio frametransmitted by the base station for a predefined signature sequencetransmitted by the base station in association with the data which isspecific to the terminal device, and extracting the data which isspecific to the terminal device from the radio frame transmitted by basestation based on an identification of the a predefined signaturesequence.

In accordance with some embodiments the terminal device is configured tosearch for the predefined signature sequence only during time periodsdetermined in accordance with a predefined timing schedule.

In accordance with some embodiments the terminal device is configured toenter a sleep mode at times outside the time periods during which itsearches for the predefined signature sequence.

In accordance with some embodiments the terminal device is configured toenter a sleep mode in response to receiving the data which is specificto the terminal device.

In accordance with some embodiments the terminal device is configured tosearch for the predefined signature sequence within a predefinedfrequency range which is narrower than and within an operating frequencyrange of the wireless telecommunications system.

In accordance with some embodiments the data which is specific to theterminal device comprises an indication of an identity of the terminaldevice.

In accordance with some embodiments the data which is specific to theterminal device comprises user-plane data for the terminal device.

In accordance with some embodiments the data which is specific to theterminal device comprises an indication of a coding scheme for theuser-plane data for the terminal device.

In accordance with some embodiments the data which is specific to theterminal device comprises an indication of a time and/or frequency onwhich user-plane data for the terminal device is transmitted by the basestation.

In accordance with some embodiments the terminal device is configured toreceive the data which is specific to the terminal device in a packetformat for which the predefined signature sequence comprises a portionselected from the group comprising a pre-amble portion, a mid-ambleportion, a post-amble portion, a pilot portion, and a scattered pilotportion.

In accordance with some embodiments the packet format further comprisesa header portion comprising an indication of an identity of the terminaldevice.

In accordance with some embodiments the packet format further comprisesa payload portion comprising user-plane data for the terminal device.

In accordance with some embodiments the predefined signature sequence isany one of a set of predefined signature sequences which the terminaldevice is configured to search for.

In accordance with some embodiments the terminal device is configured totransmit acknowledgement signalling to the base station after successfulreceipt of the data which is specific to the second terminal.

In accordance with some embodiments the data which is specific to theterminal device comprises an instruction for the terminal device toproceed to synchronise to the frame structure transmitted by the basestation in order to receive further data in a synchronous manner, andwherein the terminal device is configured to do this in response toreceiving the instruction to do so.

In accordance with some embodiments the terminal device is furtherconfigured to receive data from the base station in a synchronousmanner.

In accordance with some embodiments the terminal device is amachine-type communication, MTC, terminal device.

In accordance with some embodiments the wireless telecommunicationssystem is based around a 3rd Generation Partnership Project, 3GPP,architecture.

In accordance with another aspect of the invention there is provided amethod of operating a terminal device in a wireless telecommunicationssystem comprising searching a radio frame transmitted by a base stationof the wireless telecommunications system for a predefined signaturesequence transmitted by the base station in association with data whichis specific to the terminal device and extracting the data which isspecific to the terminal device from the radio frame transmitted by basestation based on an identification of the predefined signature sequence,thereby receiving the data which is specific to the terminal device in anon-synchronous manner.

In accordance with another aspect of the invention there is provided anintegrated circuit for use in a terminal device for receiving data froma base station in use in a wireless telecommunications system, whereinthe integrated circuit comprises circuitry for causing the terminaldevice to receive data which is specific to the terminal device from thebase station in a non-synchronous manner by searching a radio frametransmitted by the base station for a predefined signature sequencetransmitted by the base station in association with the data which isspecific to the terminal device, and extracting the data which isspecific to the terminal device from the radio frame transmitted by basestation based on an identification of the a predefined signaturesequence.

It will be appreciated that features and aspects of the inventiondescribed above in relation to the first and other aspects of theinvention are equally applicable and may be combined with the respectiveother aspects of the invention as appropriate.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the present invention will now be described by way ofexample only with reference to the accompanying drawings where likeparts are provided with corresponding reference numerals and in which:

FIG. 1 is a schematic diagram illustrating a conventional mobiletelecommunications system;

FIG. 2 is a schematic diagram illustrating a conventional LTE downlinkradio frame;

FIG. 3 is a schematic diagram illustrating a conventional LTEsynchronisation and camp-on procedure;

FIG. 4 is a schematic diagram illustrating a telecommunications systemaccording to an embodiment of the present invention;

FIG. 5 is a schematic diagram illustrating downlink data in accordancewith an embodiment of the present invention;

FIGS. 6A to 6D are schematic diagrams illustrating portions of an LTEdownlink radio frame in accordance with some embodiments of the presentinvention.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Embodiments of the present invention are described herein withparticular reference to an example implementation in a wirelesscommunication system based around the 3GPP Long Term Evolution (LTE)standard. It will, however, be appreciated that embodiments of theinvention may also be implemented in wireless telecommunications systemsbased on other standards having corresponding characteristics to thosediscussed below in the context of an LTE-type network.

FIG. 1 provides a schematic diagram illustrating some basicfunctionality of a mobile telecommunications network/system 100operating in accordance with LTE principles and which may be adapted toimplement embodiments of the invention as described further below.Various elements of FIG. 1 and their respective modes of operation arewell-known and defined in the relevant standards administered by the3GPP® body and also described in many books on the subject, for example,Holma H. and Toskala A [1]. It will be appreciated that operationalaspects of the telecommunications network which are not specificallydescribed below may be implemented in accordance with any knowntechniques, for example according to the relevant standards.

The network 100 includes a plurality of base stations 101 connected to acore network 102. Each base station provides a coverage area 103 (i.e. acell) within which data can be communicated to and from terminal devices104. Data is transmitted from base stations 101 to terminal devices 104within their respective coverage areas 103 via a radio downlink. Data istransmitted from terminal devices 104 to the base stations 101 via aradio uplink. The core network 102 routes data to and from the terminaldevices 104 via the respective base stations 101 and provides functionssuch as authentication, mobility management, charging and so on.Terminal devices may also be referred to as devices, terminals, mobilestations, user equipment (UE), user terminal, mobile radio, LTE devicesand so forth. Base stations may also be referred to as transceiverstations/nodeBs/e-nodeBs, and so forth.

Mobile telecommunications systems such as those arranged in accordancewith the 3GPP defined Long Term Evolution (LTE) architecture use anorthogonal frequency division modulation (OFDM) based interface for theradio downlink (so-called OFDMA) and a single-carrier frequency divisionmultiple access based interface for the radio uplink (so-calledSC-FDMA). FIG. 2 shows a schematic diagram illustrating an OFDM-basedLTE downlink radio frame 201. The LTE downlink radio frame istransmitted from an LTE base station (known as an enhanced Node B) andlasts 10 ms.

A downlink frame is made up of 10 subframes 202 each of which arecomposed of two slots 203. Each subframe comprises a predeterminednumber of symbols which are transmitted over a 1 ms period. Each symbolcomprises a predetermined number of orthogonal sub-carriers distributedacross the bandwidth of the downlink radio carrier.

The radio frame of FIG. 2 comprises various elements (represented not toscale in FIG. 2), such as reference symbols 204 interspersed throughouttime and frequency, synchronisation signals 205 arranged across acentral portion of the carrier bandwidth, a physical broadcast channel(PBCH) 206 arranged across a central portion of the carrier bandwidth, acontrol region 207 arranged across the full carrier bandwidth andincluding a physical control format indicator channel (PCFICH), aphysical HARQ indicator channel (PHICH), and a physical downlink controlchannel (PDCCH), and a physical downlink shared channel (PDSCH) 208arranged across the full system bandwidth.

Also schematically represented in FIG. 2 are some example resourceallocations 211, 212 for two terminals UE1, UE2. For example, theresource allocation 211 for the first terminal (UE1) extends over arange of frequencies towards the top of the carrier bandwidth in thefourth subframe, while the resource allocation 212 for the secondterminal (UE2) extends over a range of frequencies towards the bottom ofthe carrier bandwidth in the seventh and eighth subframes.

The reference symbols are uniformly distributed throughout the frame andare used for channel estimation, cell selection, handover etc.

Synchronisation signals are transmitted at the end of slots 1 and 11 ofa frame and are made up of primary (PSS) 209 (schematically shown withhatching in FIG. 2) and secondary synchronisation (SSS) (schematicallyshown with heavy shading) synchronisation signals. As is conventionalthe synchronisation signalling 209, 210 is used by terminal devices toachieve frame synchronisation and determine the physical layer cellidentity of the enhanced Node B transmitting the downlink signal.

The PBCH is allocated resources in the second slot of each radio frameand is used to broadcast the Master Information Block (MIB), whichcontains information on the downlink channel bandwidth.

Control channel data is transmitted in a control region of the subframecomprising the first n symbols of the subframe where n can vary betweenone and three symbols for channel bandwidths of 3 MHz or greater andwhere n can vary between two and four symbols for a channel bandwidth of1.4 MHz. The data transmitted in the control region includes datatransmitted on the PDCCH, the PCFICH and the PHICH. These channelstransmit physical layer control information.

PDCCH contains control data indicating which sub-carriers of thesubframe have been allocated to specific LTE terminals. This may bereferred to as physical-layer control signalling/data. Thus, the PDCCHdata transmitted in the control region of the fourth subframe shown inFIG. 2 would indicate that UE1 has been allocated the block of resourcesidentified by reference numeral 211, and the PDCCH data transmitted inthe control region of the seventh and eighth subframes would indicatethe that UE2 has been allocated the respective parts of the block ofresources identified by reference numeral 212 for the respectivesubframes. Although resource allocations for only two example devicesare shown in FIG. 2, it will of course be appreciated that in generalthere will be more terminal devices receiving data on more (if not all)of the available PDSCH resources.

PCFICH contains control data indicating the size of the control region(i.e. between one and three symbols for channel bandwidths of 3 MHz orgreater).

PHICH contains HARQ (Hybrid Automatic Request) data indicating whetheror not previously transmitted uplink data has been successfully receivedby the network.

Data transmitted to individual LTE terminals on the PDSCH can betransmitted in other resource elements of the subframe. In general PDSCHconveys a combination of user-plane data and non-physical layercontrol-plane data (such as Radio Resource Control (RRC) and Non AccessStratum (NAS) signalling). The user-plane data and non-physical layercontrol-plane data conveyed on PDSCH may be referred to as higher layerdata (i.e. data associated with a layer higher than the physical layer).

FIG. 3 illustrates an LTE “camp-on” process, that is, the processfollowed by a conventional LTE-type terminal device (i.e. a devicecompliant with the current LTE standards) to allow the device to decodedownlink transmissions which are sent by a base station via a downlinkchannel. Using this process, the terminal can identify the parts of thetransmissions that include system information for the cell and thusdecode configuration information for the cell.

As can be seen in FIG. 3, in the conventional LTE camp-on procedure, aterminal first synchronizes with the radio frame transmitted by a basestation (steps 300 and 301) using the PSS and SSS in the centre band andthen decodes PBCH (step 302). Once the terminal has performed steps 300,301 and 302, it is synchronized with the base station and ready to begindecoding other physical channels.

For each subframe, the terminal then decodes the PCFICH which isdistributed across the entire bandwidth of carrier (step 303). Theterminal then ascertains the PHICH locations (step 304) and decodes thePDCCH (step 305), in particular for identifying system informationtransmissions and for identifying its personal allocation grants. Theallocation grants are used by the terminal to locate system informationand to locate its data on the PDSCH. Both system information andpersonal allocations are transmitted on PDSCH and scheduled within thecarrier bandwidth. The terminal can then decode the PDSCH (step 306)which contains system information or data transmitted for this terminal.

As discussed above, a conventional LTE terminal device waking from a DRXsleep period will in general need to perform steps corresponding to atleast some of those shown in FIG. 3. Furthermore, it may do this only tofind there is not currently any data to be transmitted to the terminaldevice (i.e. there are no resource allocations for the terminal deviceor corresponding user-plane data on PDCCH/PDSCH). If there are no datato be received by the terminal device when it wakes up, undertaking the“wake-up” represents what is in effect a waste of the terminal device'sresources, and in particular its available power. As noted above, thepotentially unnecessary power consumption associated with waking up froma DRX cycle when there are no data to be received can be a particularproblem for certain types of terminal device, for example machine typecommunication devices, whereas the approach of FIG. 3 may be a preferredapproach for other types of terminal device, for example conventionalterminal devices.

To address this issue, some embodiments of the invention propose anapproach whereby a base station of a wireless telecommunications systemis configured to communicate in a different manner with different typesof terminal device. In particular, a base station may be configured tocommunicate data which is specific to a terminal device of a first type(e.g. a conventional terminal device) in a conventional synchronousmanner (using the conventional synchronisation procedure discussedabove), but to communicate data specific to a second terminal device ofa second type (e.g. an MTC terminal device) in a non-synchronous manner(i.e. without using the conventional synchronisation procedure discussedabove).

FIG. 4 schematically shows a wireless telecommunications system 400according to a first example embodiment of the invention. Thetelecommunications system 400 in this example is based broadly on anLTE-type architecture. As such many aspects of the operation of thetelecommunications system 400 are standard and well understood and arenot described here in detail in the interest of brevity. Operationalaspects of the telecommunications system 400 which are not specificallydescribed herein may be implemented in accordance with any knowntechniques, for example according to the LTE-standards.

The telecommunications system 400 comprises a core network part (evolvedpacket core) 401 coupled to a radio network part. The radio network partcomprises a base station (evolved-nodeB) 402, a first terminal device403 and a second terminal device 405. It will of course be appreciatedthat in practice the radio network part may comprise a plurality of basestations serving a larger number of terminal devices across variouscommunication cells. However, only a single base station and twoterminal devices are shown in FIG. 4 in the interests of simplicity.

The terminal devices 403 and 405 are arranged to communicate data to andfrom the base station (transceiver station) 402. The base station is inturn communicatively connected to a serving gateway, S-GW, (not shown)in the core network part which is arranged to perform routing andmanagement of mobile communications services to the terminal devices inthe telecommunications system 400 via the base station 402. In order tomaintain mobility management and connectivity, the core network part 401also includes a mobility management entity (not shown) which manages theenhanced packet service (EPS) connections with the terminal devices 403and 405 operating in the communications system based on subscriberinformation stored in a home subscriber server, HSS. Other networkcomponents in the core network (also not shown for simplicity) include apolicy charging and resource function (PCRF) and a packet data networkgateway (PDN-GW) which provides a connection from the core network part401 to an external packet data network, for example the Internet. Asnoted above, the operation of the various elements of the communicationssystem 400 shown in FIG. 4 may be broadly conventional apart from wheremodified to provide functionality in accordance with embodiments of theinvention as discussed herein.

In this example, it is assumed the first terminal device 403 is aconventional smart-phone type terminal device communicating with thebase station 402. Thus this first terminal device 403 comprises atransceiver unit 403 a for transmission and reception of wirelesssignals and a controller unit 403 b configured to control the smartphone 403. The controller unit 403 b may comprise a processor unit whichis suitably configured/programmed to provide the desired functionalityusing conventional programming/configuration techniques for equipment inwireless telecommunications systems. The transceiver unit 403 a and thecontroller unit 403 b are schematically shown in FIG. 4 as separateelements. However, it will be appreciated that the functionality ofthese units can be provided in various different ways, for example usinga single suitably programmed integrated circuit. As will be appreciatedthe smart phone 403 will in general comprise various other elementsassociated with its operating functionality.

In this example, it is assumed the second terminal device 405 is amachine-type communication (MTC) terminal device operating in accordancewith an embodiment of the invention. As discussed above, these types ofterminal device may be typically characterised as semi-autonomous orautonomous wireless communication terminal devices communicating smallamounts of data. Examples include so-called smart meters which, forexample, may be located in a customer's house and periodically transmitinformation back to a central MTC server data relating to the customer'sconsumption of a utility such as gas, water, electricity and so on. MTCterminal devices may in some respects be seen as terminal devices whichcan be supported by relatively low bandwidth communication channelshaving relatively low quality of service (QoS), for example in terms oflatency. It is envisaged that these kinds of device might beubiquitously deployed without access to a permanent power supply andwithout regular human monitoring (i.e. without someone to “charge” theterminal device when its power is low). This is why these types ofdevice can be significantly impacted by the above-described relativelypower intensive procedure for waking a conventional terminal device froma DRX sleep mode.

As with the smart phone 403, the MTC terminal device 405 comprises atransceiver unit 405 a for transmission and reception of wirelesssignals and a controller unit 405 b configured to control the MTCterminal device 405. The controller unit 405 b may comprise a processorunit which is suitably configured/programmed to provide the desiredfunctionality described herein using conventionalprogramming/configuration techniques for equipment in wirelesstelecommunications systems. For example, the functionality of thecontroller unit 405 b may be provided by an integrated circuit accordingto an embodiment of the invention. The controller unit 405 b may, forexample, comprise various functional units associated with variousfunctions to be performed in accordance with the principles describedherein. The transceiver unit 405 a and the controller unit 405 b areschematically shown in FIG. 4 as separate elements for ease ofrepresentation. However, it will be appreciated that the functionalityof these units can be provided in various different ways followingestablished practices in the art, for example using a single suitablyprogrammed integrated circuit. It will be appreciated the MTC terminaldevice 405 will in general comprise various other elements associatedwith its operating functionality which are not shown here in theinterests of simplicity (for example, the MTC terminal device 405 mayfurther comprise a user interface and so forth).

The base station 402 comprises a transceiver unit 402 a for transmissionand reception of wireless signals and a controller unit 402 b configuredto control the base station 402. The controller unit 402 b may comprisea processor unit which is suitably configured/programmed to provide thedesired functionality described herein using conventionalprogramming/configuration techniques for equipment in wirelesstelecommunications systems. The transceiver unit 402 a and thecontroller unit 402 b are schematically shown in FIG. 4 as separateelements for ease of representation. However, it will be appreciatedthat the functionality of these units can be provided in variousdifferent ways following established practices in the art, for exampleusing a single suitably programmed integrated circuit. It will beappreciated the base station 402 will in general comprise various otherelements associated with its operating functionality.

Thus, the base station 402 is configured to communicate data with thesmart phone 403 over a first radio communication link 404 andcommunicate data with the MTC terminal device 405 over a second radiocommunication link 406.

It is assumed here the base station 402 is configured to communicatewith the smart phone 403 over the first radio communication link 404 inaccordance with the established principles of LTE-based communications.

To communicate terminal-device specific data between the base station402 and the conventional smart phone terminal device 403, the smartphone 403 first synchronises with the base station 402 in accordancewith the above-described techniques. The base station 402 may thencommunicate data intended for the smart phone 403 in a synchronousmanner in accordance with established techniques.

In a conventional LTE system an MTC terminal device will typically berequired to undertake a synchronisation and camp-on procedure which issimilar to that of a conventional smart phone in order to communicatedevice-specific data with the base station. As discussed above, this canbe problematic for maintaining power reserves. Accordingly, embodimentsof the present invention provide an approach that allows certain typesof terminal device, for example MTC terminal devices, to receive usefuldata without the same overheads associated with the conventionalsynchronisation procedure associated with other types of terminaldevice. Furthermore, in accordance with some embodiments of theinvention this is achieved in a manner that does not impact the abilityof the other types of terminal device (for example,conventionally-operating legacy terminal devices) to function in thetelecommunications system without modification.

This may be achieved in accordance with some embodiments of theinvention by avoiding the process of detecting and decoding theconventional synchronisation and control signalling before communicatingterminal device-specific data with certain types of terminal device,such as MTC terminal devices. More specifically, in accordance with someembodiments of the invention, when a terminal device wakes to seek toreceive any data that might be pending from a base station after aperiod of inactivity, the terminal device employs an alternative methodthat does not include the above-described frame synchronisation.

Thus in the wireless telecommunications system 400 shown in FIG. 4, theMTC terminal device 405 is configured to switch between a sleep mode andan awake mode based on a predetermined timing schedule. This aspect ofthe wireless telecommunications system may broadly follow the sameprinciples as for the conventional DRX scheme, although it is expectedthat the maximum periods of inactivity may be longer than currentlyavailable for DRX, for example several minutes, hours or even days.However, on waking up in accordance with the predefined timing schedule,instead of seeking to synchronise to the frame structure transmitted bya base station in accordance with conventional techniques, the MTCterminal device 405 according to an embodiment of the invention insteadstarts searching for a predefined signature sequence which istransmitted by a base station according to an embodiment of theinvention in association with terminal-specific data, such as user planedata for the MTC terminal device 405, or other data which is not genericcontrol signalling.

In accordance with this embodiment of the invention, the base station402 shown in FIG. 4 is configured to transmit the predefined signaturesequence in association with terminal specific data using a packetformat such as schematically shown in FIG. 5. The packet 500schematically represented in FIG. 5 comprises three main portions,namely a preamble portion 501, a header portion 502, and a payloadportion 503. The packet itself may be coded in accordance with theestablished principles for communicating data in wirelesstelecommunications systems. In this example embodiment a relatively loworder modulation scheme, for example QPSK, might be used to help improvereception ability across an operating cell for the base station.However, in other embodiments other modulation schemes could be used.The preamble portion 501 of the packet 500 comprises the predefinedsignature sequence, the header portion 502 comprises an indication of anidentity of a terminal device for which terminal-device specific data isto be transmitted in the subsequent payload portion 503, and the payloadportion 503 comprises the terminal-specific data.

Thus, the MTC terminal device 405 is configured to search the signalreceived from the base station to seek to identify the presence of thepredefined signature sequence. On detection of an occurrence of thepredefined signature sequence (preamble) 501 in the signal transmittedby the base station 402 in accordance with an embodiment of theinvention, the terminal device 405 proceeds to decode the followingheader portion to determine whether the data is intended for itselfbased on the identity of the terminal device(s) indicated in the headerportion. Terminal devices may be identified in accordance with anyestablished techniques, for example based on a conventional radionetwork identifier for the terminal device. The header portion 502 maybe coded using a predefined coding scheme to aid decoding without anyprior signalling. If a terminal device identifies from the headerportion that the packet 500 comprises data addressed to the terminaldevice, the terminal device may then continue to decode and extract therelevant data from the payload portion 503. In some exampleimplementations the payload portion might always be coded in accordancewith a predefined scheme. In other implementations where the payloadportion 503 may be coded differently at different times, for exampleusing different coding rates, an indication of the relevant codingscheme may be included in the header portion to aid the terminal devicesin decoding the corresponding payload portion 503. If the terminaldevice determines from the header portion 502 that the payload data isnot intended for the terminal device, the terminal device may continuesearching for other currencies of the predefined signature sequence 501for the remainder of its awake period according to the predefined timingschedule, before returning to a sleep mode. Accordingly, when the basestation 402 acquires data intended for the terminal device 405, it maybe configured to buffer the data until the next (or later) time periodduring which the terminal device is configured to wake up and beginsearching for the predefined signature sequence. When this periodarrives, the base station 402 may be configured to transmit a packethaving the format represented in FIG. 5 in order to communicate the datato the terminal device within the known wake-up window for the terminaldevice.

The base station 402 may be configured to introduce the packet 500 at anarbitrary location within the frame structure employed by the basestation 402 for communicating with other terminal devices in aconventional synchronous manner, for example such as the frame structureschematically represented in FIG. 2. However, it will generally besimpler if the base station introduces the packet 500 at a locationwhich does not significantly interfere with this frame structure. Forexample, it may be advantageous for the base station 402 to introducethe packet(s) 500 at times and frequencies which are outside regions forcontrol signalling associated with other terminal devices, and areinstead in regions which the base station is otherwise free to scheduleas desired. In particular, it may be advantageous for the packet(s) 500to be scheduled by the base station during regions of the framestructure used for communicating synchronously with conventionalterminal devices on PDSCH, thereby avoiding interference with controlsignalling for other terminal devices, such as signalling associatedwith PSS, SSS, PBCH, PDCCH, PCFICH and/or PHICH. Accordingly, when thebase station transmits a packet 500 for communicating non-synchronouslywith terminal devices of one type at a time and frequency correspondingto a region of PDSCH in the frame structure associated withcommunications with conventional terminal devices, the base station mayavoid scheduling conventional terminal devices at these times andfrequencies.

Thus, in broad summary of some embodiments of the invention, data forcertain types of terminal device may be communicated to those terminaldevices in a non-synchronous manner in a wireless telecommunicationsnetwork which also supports synchronous communications for other typesof terminal device. In particular, this may be done by communicatingdata specific to a particular terminal device in association with apredefined signature sequence transmitted by a base station, for examplea preamble, which the terminal devices are configured to search for. Onidentifying an occurrence of the predefined signature sequence aterminal device may proceed to decode the data transmitted by the basestation in association with the signature sequence. Thus the terminaldevice is able to receive the data simply by detecting the predefinedsignature sequence in a nonsynchronous manner, thereby avoiding aprocess of synchronising to the frame structure of the base stationtransmissions.

It will be appreciated that within the context of the general principlesset out above there are many different ways of implementing variousaspects of a wireless telecommunications system and/or they stationand/or terminal device in accordance with various embodiments of theinvention, and some of these are now described.

FIG. 6A schematically shows one example location for a packet 500 forcommunicating non-synchronously with an MTC terminal device within aconventional LTE frame structure in accordance with an embodiment of theinvention. The example frame structure represented in FIG. 6A isemployed by a base station for communicating synchronously with otherterminal devices in a manner which is otherwise in accordance withestablished LTE standards. The extent of the frame structure representedin FIG. 6A corresponds with a single subframe 1202. Conventional aspectsof the subframe 1202 are similar to and will be understood from thecorresponding conventional aspects of the subframes 202 of thecommercial LTE frame structure represented in FIG. 2. In this example,the packet 500 for communicating non-synchronously occupies a contiguousregion in the time-frequency resource grid of the frame structure. Therange of frequencies spanned by the packet 500 may be predefined andselected according to the implementation at hand (for example, how muchdata needs to be communicated for asynchronously-operating devices). Forexample, a width of 1.4 MHz might be used.

The location of the packet 500 in frequency space may be fixed, forexample in accordance with a defined standard or through priornegotiation between the base station and a terminal device configured tooperate in accordance with an embodiment of the invention. For example,a frequency band within the overall carrier bandwidth for use fornon-synchronous communication in accordance with embodiments of theinvention may be established during an initial camp on procedure orthrough dedicated signalling. Thus, where transmission ofnon-synchronous communications are restricted to a limited bandwidthwithin the overall carrier bandwidth, a terminal device searching forthe predefined signature sequence need only scan within the predefinedrestricted frequency range. However, in other examples, a packet bearingdata to be transmitted non-synchronously may be inserted into the framestructure by the base station at any frequency. In this case terminaldevices searching for the predefined signature sequence may search theentire frequency space. In some cases, the base station may beconfigured to update the terminal devices on the potential locations offuture predefined signature sequence transmissions (e.g. in terms ofparticular frequency ranges), thereby simplifying the process ofsearching. For example, this may be communicated in a header portion ofa packet 500 of the kind discussed above.

The location of the packing 500 in time may be arbitrarily selected bythe base station. This is because the terminal device searching for thepacket 500 is not synchronised to the frame structure and so it does notmatter to the terminal device when the packet is transmitted relative tothe existing LTE frame structure used for communicating with otherterminal devices. However, the base station may be configured to insertthe non-synchronous communications in a way which minimises any impacton communications with conventional LTE terminal devices within theexisting frame structure.

Thus, in the example shown in FIG. 6A, the packet 500 is inserted by thebase station outside of the times and frequencies corresponding to acontrol region 1207 (PDCCH) associated with the LTE frame structure. Inthe example of FIG. 6A the asynchronous communications packet 500 isinserted by the base station into the existing LTE frame structure insymbols occurring immediately after the control region 1207. Thus thebase station is operable to synchronise the packet to a selectedlocation in the existing LTE frame structure which is outside thecontrol region use for communicating control data to other conventionaldevices in order to minimise any impact on these other devices. However,as noted above terminal devices searching for the packet 500 may not beaware that it has any particular synchronisation to the frame structure.On the contrary, these terminal devices simply search for the existenceof the predefined signature sequence anywhere within the signaltransmitted by the base station. (The process of searching for thepredefined sequence may be performed in accordance with any knowntechniques, for example using similar techniques to those currently usedfor identifying the PSS and SSS signalling)

As represented in FIG. 6A, the extent of the asynchronous communicationpacket 500 in the LTE frame structure encompasses one of theconventional LTE reference symbols 1204. In particular, the payload dataportion 503 encompasses one of the reference symbols 1204. In this case,the base station may simply transmit data specific to the terminaldevice(s) receiving the packet (e.g. based on identification informationin the header portion 502 as discussed above) in place of the referencesymbols. This will cause conventional LTE devices expecting to see thereference symbol to conclude there was an error in transmission andreact accordingly (e.g. by ignoring the reference symbol andinterpolating from other reference symbols). Alternatively, the basestation may be configured to transmit the reference symbol 1204occurring within the payload data portion of the packet 500 in the usualway. In this case the terminal device(s) asynchronously receiving thepacket 500 might be configured to ignore this portion of the payloaddata. This may be based, for example, on ensuring that any referencesymbols encompassed by the packet 500 occur at a predefined location inthe payload data/packet, or at locations which are signalled to theterminal device in the header portion 502 to indicate which parts of thepayload data region 503 the terminal device should ignore. In principlethe extent of the packet may be sufficient to span more than onesubframe. In this case, the packet will overlap a PDCCH region of atleast one subframe. The terminal device may be provided with anindication of the location of the PDCCH symbols that are overlapped toavoid the terminal device attempting to decode these regions.

Thus, as described above, a terminal device according to an embodimentof the invention, such as the MTC device 405 schematically representedin FIG. 4, is configured to awake from a sleep mode and begin searchingfor the predefined signature sequence, the searching process maycontinue until a specified event, for example the expiration of theterminal device's wake-up window or the successful reception ofdevice-specific data. On identifying the signature sequence 501transmitted from the base station, the MTC device 405 proceeds to decodethe immediately following header portion 502. As discussed above, theheader portion 502 may contain information relating to the identity ofthe terminal device with which the base station is seeking tocommunicate device-specific data to and information on the coding schemeused for the device-specific data in the following payload portion 503.If the terminal device determines from the header portion 502 that thepayload data 503 is intended for itself, it will proceed to decode thefollowing payload portion 503 so as to extract the relevant data.

In some cases the device-specific information which the base stationwishes to communicate may be intended for only a single terminal device,in which case the header portion 502 may comprise an indication of anidentity that is unique to that device. In other situations, theterminal-device specific information may be specific to a class ofterminal devices. For example, the terminal-device specific informationmay comprise price update information for communicating to a pluralityof MTC devices acting as smart-meters in a consumer's home. In suchcases the header portion 502 may include an identifier for a group ofdevices, for example a broadcast address, such that devices which aremembers of the group are able to identify the packet has been intendedfor themselves. This allows for simultaneous non-synchronouscommunication between a base station and a plurality of devices.Furthermore, it will be appreciated that while FIG. 6A shows only asingle non-synchronous communication packet 500 for the sake ofsimplicity, in other examples where a base station is tonon-synchronously communicate different data to a plurality of differentterminal devices there may be multiple instances of nonsynchronouscommunications packets of the kind shown in FIG. 6A inserted in a singlesubframe.

It will be appreciated that in some implementations the predefinedsignature sequence itself may provide the relevant identifier for theterminal device to which the data is intended. For example, eachindividual terminal device may be associated with a specific predefinedsignature sequence so that if the terminal device identifies itssignature sequence it knows the subsequent data is intended for theterminal device. In practice this is unlikely to be an optimum approachwhere there are a large number of terminal devices which mightasynchronously receive data because of the correspondingly large numberof predefined signature sequences that would need to be defined.However, where terminal devices may be classified into groups (forexample, all smart meters owned by a certain provider), a dedicatedsignature sequence may be used to address this group. This would avoidthe need for including any identity information in a header portion.Furthermore, if the payload data is transmitted in association with thepredefined signature sequence using a predefined coding scheme, therewould be very little information needed by the terminal devices to allowthem to decode the payload data once they have identified the predefinedsignature sequence. Thus, a header portion might not be employed.

FIGS. 6B, 6C and 6D schematically shows other example locations for apacket 500 for communicating non-synchronously with MTC terminal deviceswithin a conventional LTE frame structure in accordance with anembodiment of the invention. These figures are similar to, and will beunderstood from the corresponding description of FIG. 6A discussedabove.

FIG. 6B differs from FIG. 6A in that it shows the packet 500 beingtransmitted at a different portion of the subframe 1207. In the exampleshown in FIG. 6B, the non-synchronous communications packet 500 isschematically shown being inserted into the LTE frame by the basestation at an arbitrary time which is not synchronised with the existingLTE frame structure. Whilst this approach is in principle possible, itcan potentially complicate the scheduling requirements for the basestation and so may not be a preferred approach in practice.

FIG. 6C differs from FIG. 6A in that the packet 500 is not transmittedin a contiguous block. In the example shown in FIG. 6C, the predefinedsignature sequence (preamble portion) 501 and header portion 502 arebroadcast at broadly the same locations as shown in FIG. 6A. However,the payload portion 503 is transmitted at a time and frequency that isnot contiguous with the header portion 502. The location of the payloadportion 503 relative to the header portion 502 may be indicated in theheader portion 502 or predefined/pre-established. This approach providesmore flexibility on where the base station can insert the signallingassociated with non-synchronous communications but at the cost ofincreased complexity.

FIG. 6D differs from FIG. 6A in that the packet 500 is of a shorterduration and does not overlap with any reference symbols of the existingLTE frame structure, thereby simplifying the decoding process.

It will be appreciated that a base station might only insert packetscorresponding to packet 500 for non-synchronous communication withterminal devices in subframes where there are data that the base stationwishes to communicate to terminal devices in a nonsynchronous manner andwhere the base station is aware recipient terminal device will not be ina sleep mode, e.g. based on a predefined/pre-negotiated timing scheduleas discussed above. In examples where the base station is aware of thewake-up periods for the terminal device with which it wishes tocommunicate asynchronously, it may be configured to avoid transmittingthe data at times which are close to the opening/closing of the terminaldevices wake-up window. This is to allow for drifts in the clock of theterminal device relative to the base station which might cause theterminal device to wake slightly before or after the base station'sunderstanding of when the awake window is occurring.

In some embodiments a base station may not be aware of the sleep/wakecycle for a terminal device with which the base station wishes tonon-synchronously communicate data in accordance with an embodiment ofthe invention. In this situation a base station may be configured tosimply attempt to communicate the data at a selected time and rely onacknowledgement signalling from the terminal device to indicate whetheror not the data has been successfully received, for example based aroundexisting HARQ techniques. Thus, if the base station transmits therelevant data during a time when the terminal devices in a sleep mode,the base station will not receive an acknowledgement, and may attemptretransmission at a later time. If, on the other hand, the base stationtransmits the relevant data during a time when the terminal device isawake and searching for the predefined signature sequence and theterminal device successfully receives the data, the terminal device maybe configured to transmit acknowledgement signalling to the base stationto indicate this. The acknowledgment signalling may be transmitted bythe terminal device at a predefined temporal offset relative to the timethe packet to be acknowledged was received. This allows the terminaldevice to in effect send acknowledgment signalling which is synchronisedto the frame structure (i.e. by using timing relative to the receipt ofthe predefined signature sequence which is itself synchronised to theframe structure by base station driven scheduling).

Whiles acknowledgment signalling may be helpful in some circumstances,in some cases where acknowledgment signalling might in principle behelpful, it might not be utilised in order to reduce two-waycommunications between the base station and the terminal device. In thissituation the base station might use other methods to increase thechance of the terminal device successfully receiving data, for exampleemploying routine retransmissions. However, in practice this approachmay not be desirable because the base station may not be able toestablish to adequate degree of certainty the success of a transmission.

In accordance with embodiments of the invention, a base station maycommunicate with a terminal device only relatively infrequently, forexample based on the terminal devices sleep/wake cycle. It is thereforepossible for a base station to accrue multiple messages that needs to becommunicated to the terminal device. Accordingly, the base station maybuffer these for transmission in a single payload portion (to the extentthe available payload portion is large enough).

In accordance with the embodiment of the invention discussed above, thepredefined signature sequence comprises a preamble of a non-synchronouscommunications packet 500. However, in other examples it will beappreciated that other forms of predefined signature sequence may beemployed. For example, the predefined signature sequence may comprise amid-amble or post amble of a packet. The predefined signature sequencemay also comprise a different form of pilot signal, for example spanninga limited frequency range for the entire duration of a non-synchronoustransmission, or scattered throughout a non-synchronous transmission. Aterminal device identifying such a pilot signal may be configured todecode associated data based on a predefined/pre-negotiated relationshipbetween the presence and location of the pilot signal and surroundingtime/frequency resources, for example.

Thus to summarise some embodiments of the invention, there is provided awireless telecommunications system comprising a base station, a firstterminal device and a second terminal device, wherein the first terminaldevice is a terminal device of a first type and the second terminaldevice is a terminal device of a second type, the second type beingdifferent from the first type, and wherein the at least one base stationis configured to communicate data which is specific to the firstterminal device in a synchronous manner and to communicate data which isspecific to the second terminal device in a non-synchronous manner.Embodiments of the invention also provide for a base station and aterminal device of the second type configured to operate in the wirelesstelecommunications system.

The device-specific data may include an identifier for the secondterminal device. In some examples a terminal device may be configured onreceipt of device-specific data comprising an identifier for theterminal device to undergo a conventional synchronisation procedure toreceive further data, for example user plane data, in a synchronousmanner. That is to say, the principles underlying the above-describedtechnique for communicating asynchronously with certain types ofterminal device may be employed to communicate an indication to a giventerminal device that it should synchronise with the base stationtransmissions in order to allow synchronous reception of data, forexample in accordance with conventional LTE communication techniques.Thus in this operating mode the terminal device still synchronises withthe network, but only after it has already been informed asynchronouslythat it should do so. Accordingly, by having the base station transmit apredefined signature sequence in association with device-specific datacomprising a device-specific identifier, the base station can in effectinstruct the terminal device to synchronise to the frame structure suchthat further data can be subsequently transmitted in a conventionalsynchronous manner. Accordingly, with this approach the terminal deviceis relieved of the task of synchronising with the network on everywake-up just to see if there are any data available for it. Instead, theterminal devices is first provided with an asynchronous indication thatdata are actually waiting for the terminal device, thereby helping toavoid the terminal devices synchronising with the base station whenthere are no data to be received.

Alternatively, and as described above with reference to the payloaddata, the device specific data may comprise user-plane data which thebase station wishes to communicate to the device so that the terminaldevices able to receive the user plane data without having tosynchronise to the base station at all. This may be most appropriatewhen there will typically only be relatively small amounts of data to betransmitted to the terminal device. Where it is expected that largeramounts of data will be sporadically transmitted to the device, anapproach in which the device-specific data comprises an instructioninforming the terminal device to synchronise to receive further data maybe preferred.

In a wireless telecommunications system according to an embodiment ofthe invention, a plurality of predefined signature sequences may bedefined for use for asynchronously transmitting data in the mannerdescribed above. Each terminal device configured to receive dataasynchronously may be configured to search for any of, or any of asubset of, these predefined signature sequences.

It will be appreciated that various modifications can be made to theembodiments described above without departing from the scope of thepresent invention as defined in the appended claims. In particularalthough embodiments of the invention have been described primarily withreference to an LTE-based telecommunications system/mobile radionetwork, it will be appreciated that the present invention can beapplied to other forms of network such as GSM, 3G/UMTS, CDMA2000, etc.,where similar issues can arise.

Further particular and preferred aspects of the present invention areset out in the accompanying independent and dependent claims. It will beappreciated that features of the dependent claims may be combined withfeatures of the independent claims in combinations other than thoseexplicitly set out in the claims.

REFERENCES

-   [1] Holma H. and To Skala A, “LTE for UMTS OFDMA and SC-FDMA based    radio access”, John Wiley and Sons, 2009.-   [2] ETSI TS 122 368 V10.530 (2011-07)/3GPP TS 22.368 version 10.5.0    Release 10)

1. A wireless telecommunications system comprising at least one basestation, a first terminal device and a second terminal device, whereinthe first terminal device is a terminal device of a first type and thesecond terminal device is a terminal device of a second type, the secondtype being different from the first type, and wherein the at least onebase station is configured to communicate data which is specific to thefirst terminal device in a synchronous manner and to communicate datawhich is specific to the second terminal device in a non-synchronousmanner.
 2. The wireless telecommunications system of claim 1, whereinthe at least one base station is configured to communicate data which isspecific to the second terminal device in a non-synchronous manner onlyduring time periods determined in accordance with a predefined timingschedule.
 3. The wireless telecommunications system of claim 1, whereinthe at least one base station is configured to communicate data which isspecific to the second terminal device in a non-synchronous manner usinga predefined frequency range which is narrower than and within anoperating frequency range for the at least one base station.
 4. Thewireless telecommunications system of claim 1, wherein the data which isspecific to the second terminal device comprises an indication of anidentity of the second terminal device.
 5. The wirelesstelecommunications system of claim 1, wherein the data which is specificto the second terminal device comprises user-plane data for the secondterminal device.
 6. The wireless telecommunications system of claim 5,wherein the data which is specific to the second terminal devicecomprises an indication of a coding scheme for the user-plane data forthe second terminal device.
 7. The wireless telecommunications system ofclaim 1, wherein the data which is specific to the second terminaldevice comprises an indication of a time and/or frequency on whichuser-plane data for the second terminal device is transmitted by the atleast one base station.
 8. The wireless telecommunications system ofclaim 1, wherein the at least one base station is configured tocommunicate data which is specific to the second terminal device in anon-synchronous manner by transmitting said data in association with apredefined signature sequence.
 9. The wireless telecommunications systemof claim 8, wherein the at least one base station is configured totransmit the data which is specific to the second terminal device in apacket format for which the predefined signature sequence comprises aportion selected from the group comprising a pre-amble portion, amid-amble portion, a post-amble portion, a pilot portion, and ascattered pilot portion.
 10. The wireless telecommunications system ofclaim 9, wherein the packet format further comprises a header portioncomprising an indication of an identity of the second terminal device.11. The wireless telecommunications system of claim 9, wherein thepacket format further comprises a payload portion comprising user-planedata for the second terminal device.
 12. The wireless telecommunicationssystem of claim 11, wherein the packet format further comprises anindication of resources encompassed by the payload portion of the packetwhich are not used to convey the data which is specific to the secondterminal device.
 13. The wireless telecommunications system of claim 8,wherein the at least one base station is configured to communicate datawhich is specific to another terminal device in a non-synchronous mannerby transmitting said data specific to said another terminal device inassociation with the predefined signature sequence.
 14. The wirelesstelecommunications system of claim 8, wherein the at least one basestation is configured to communicate data which is specific to anotherterminal device in a non-synchronous manner by transmitting said dataspecific to said another terminal device in association with anotherpredefined signature sequence.
 15. The wireless telecommunicationssystem of claim 8, wherein the predefined signature sequence is one of aset of predefined signature sequences for use by the at least one basestation for non-synchronously communicating data with terminal devicesof the second type.
 16. The wireless telecommunications system of claim15, wherein the predefined signature sequence is one of a subset of theset of predefined signature sequences, and wherein the base station isconfigured to select one of the subset of the set of predefinedsignature sequences to be used for non-synchronously communicating datawith the second terminal device.
 17. The wireless telecommunicationssystem of claim 8, wherein the second terminal device is configured tosearch transmissions from the at least one base station to identity thepredefined signature sequence and to determine if an identifiedtransmission of the predefined signature sequence is associated withdata which is specific to the second terminal device.
 18. The wirelesstelecommunications system of claim 1, wherein the second terminal deviceis configured to transmit acknowledgement signalling to the at least onebase station after successful receipt of the data which is specific tothe second terminal.
 19. The wireless telecommunications system of claim18, wherein the second terminal device is configured to transmit theacknowledgement signalling a predefined time after receiving thepredefined signature sequence.
 20. The wireless telecommunicationssystem of claim 1, wherein the at least one base station is configuredto transmit a radio frame structure including a control region forcontrol data for terminal devices of the first type, and wherein the atleast one base station is configured to communicate with the secondterminal device at times and frequencies outside the control region forterminal devices of the first type.
 21. The wireless telecommunicationssystem of claim 1, wherein the data which is specific to the secondterminal device comprises an instruction for the second terminal deviceto proceed to synchronise to a frame structure transmitted by the atleast one base station in order to receive further data synchronously.22. The wireless telecommunications system of claim 1, wherein the atleast one base station is further configured to communicate data withthe second terminal device in a synchronous manner.
 23. The wirelesstelecommunications system of claim 1, wherein the second type ofterminal device is a machine-type communication, MTC, terminal device.24. The wireless telecommunications system of claim 1, wherein thewireless telecommunications system is based around a 3rd GenerationPartnership Project, 3GPP, architecture.
 25. A method of operating awireless telecommunications system comprising at least one base station,a first terminal device and a second terminal device, wherein the firstterminal device is a terminal device of a first type and the secondterminal device is a terminal device of a second type, the second typebeing different from the first type, the method comprising communicatingdata which is specific to the first terminal device in a synchronousmanner and communicating data which is specific to the second terminaldevice in a non-synchronous manner.
 26. A base station for communicatingdata with a first terminal device of a first type and a second terminaldevice of a second type, the second type being different from the firsttype, wherein the base station is configured to communicate data whichis specific to the first terminal device in a synchronous manner and tocommunicate data which is specific to the second terminal device in anon-synchronous manner.
 27. The base station of claim 26, wherein thebase station is configured to communicate data which is specific to thesecond terminal device in a non-synchronous manner only during timeperiods determined in accordance with a predefined timing schedule. 28.The base station of claim 26, wherein the base station is configured tocommunicate data which is specific to the second terminal device in anon-synchronous manner using a predefined frequency range which isnarrower than and within an operating frequency range for the basestation.
 29. The base station of claim 26, wherein the data which isspecific to the second terminal device comprises an indication of anidentity of the second terminal device.
 30. The base station of claim26, wherein the data which is specific to the second terminal devicecomprises user-plane data for the second terminal device.
 31. The basestation of claim 30, wherein the data which is specific to the secondterminal device comprises an indication of a coding scheme for theuser-plane data for the second terminal device.
 32. The base station ofclaim 26, wherein the data which is specific to the second terminaldevice comprises an indication of a time and/or frequency on whichuser-plane data for the second terminal device is transmitted by the atleast one base station.
 33. The base station of claim 26, wherein thebase station is configured to communicate data which is specific to thesecond terminal device in a non-synchronous manner by transmitting saiddata in association with a predefined signature sequence.
 34. The basestation of claim 33, wherein the data which is specific to the secondterminal device is transmitted in a packet format for which thepredefined signature sequence comprises a portion selected from thegroup comprising a pre-amble portion, a mid-amble portion, a post-ambleportion, a pilot portion, and a scattered pilot portion.
 35. The basestation of claim 34, wherein the packet format further comprises aheader portion comprising an indication of an identity of the secondterminal device.
 36. The base station of claim 34, wherein the packetformat further comprises a payload portion comprising user-plane datafor the second terminal device.
 37. The base station of claim 36,wherein the packet format further comprises an indication of resourcesencompassed by the payload portion of the packet which are not used toconvey the data which is specific to the second terminal device.
 38. Thebase station of claim 33, wherein the base station is configured tocommunicate data which is specific to another terminal device in anon-synchronous manner by transmitting said data specific to saidanother terminal device in association with the predefined signaturesequence.
 39. The base station of claim 33, wherein the base station isconfigured to communicate data which is specific to another terminaldevice in a non-synchronous manner by transmitting said data specific tosaid another terminal device in association with another predefinedsignature sequence.
 40. The base station of claim 33, wherein thepredefined signature sequence is one of a set of predefined signaturesequences for use by the base station for non-synchronouslycommunicating data with terminal devices of the second type.
 41. Thebase station of claim 40, wherein the predefined signature sequence isone of a subset of the set of predefined signature sequences, andwherein the base station is configured to select one of the subset ofthe set of predefined signature sequences to be used fornon-synchronously communicating data with the second terminal device.42. The base station of claim 26, wherein the base station is configuredto receive acknowledgement signalling from the second terminalindicating successful receipt of the data which is specific to thesecond terminal.
 43. The base station of claim 42, wherein the basestation is configured to receive the acknowledgement signalling at atime which depends on a predetermined time after transmitting thepredefined signature sequence.
 44. The base station of claim 26, whereinthe base station is configured to transmit a radio frame structureincluding a control region for control data for terminal devices of thefirst type, and wherein the base station is configured to communicatewith the second terminal device at times and frequencies outside thecontrol region for terminal devices of the first type.
 45. The basestation of claim 26, wherein the data which is specific to the secondterminal device comprises an instruction for the second terminal deviceto proceed to synchronise to a frame structure transmitted by the basestation in order to receive further data synchronously.
 46. The basestation of claim 26, wherein the base station is further configured tocommunicate data with the second terminal device in a synchronousmanner.
 47. The base station of claim 26, wherein the second type ofterminal device is a machine-type communication, MTC, terminal device.48. The base station of claim 26, wherein the wirelesstelecommunications system is based around a 3rd Generation PartnershipProject, 3GPP, architecture.
 49. A method of operating a base station ofa wireless telecommunications system for communicating data with a firstterminal device of a first type and a second terminal device of a secondtype, the second type being different from the first type, wherein themethod comprises communicating data which is specific to the firstterminal device in a synchronous manner and communicating data which isspecific to the second terminal device in a non-synchronous manner.